Effect of Aircraft Loading Program Modifications on the Fatigue Life and Damage Cumulation PartⅠ-Effect of Load Peaks in Case of Central Hole Sheet Specimens

摘要

Flight simulation and program tests were performed with dif¬ferent 2024-T3 sheet specimens containing a central hole." The ef¬fect of the peak-load frequency on the damage sum and flight number was investigated. Gust spectrum test results were compared with those of other authors. For sufficiently close spectra with similar log-linear airborne stress distribution but different GAG cycle distribution, the relative Miner rule yielded satisfactory results. In the case of truncation levels Smax = 1.84σm and Smax= 1.685σm , the investigated change of the frequency of stress cycles at the highest loading level (for cycle numbers smaller than it follows from the log-linear gust distribution) had a weak effect on the damage sum, while the effect of decrease of the frequency of the lowest stress amplitudeσa= 0.222σm(MiniTWIST instead of TWIST) was con-sierable in some cases. It was found that in particular loading pro-gram cases, rare load peaks may have not only a beneficial but also a detrimental effect on the number of simulated flights. Trunca¬tion had a detrimental effect but the increase of the number of overload peaks above the number of cycles at the truncation level as¬sociated with the log-linear gust distribution had also a detri¬mental effect.